I have several flac files which each have 2 different cover art images attached, the problem is that the media player I use (J.River Media Center) will only read the first image in the tag and the image i would like to be displayed is the second one attached. How can I swap these two images?

I was really looking for something that could work with around 500 different files at once. Each file has one artwork in common, but one another one individual to each file. I was hoping to create an action that would make sure the common artwork was all put into the second slot while the individual one was in the first slot for each song.